A pneumatic tire is a laminate, composite structure having an open toroidal-like shape. The toroidal-like shape includes a so-called carcass, which contains numerous components, to which a belt package and/or reinforcement and a tread are added to form the tire. Each of the carcass, belt package, and tread is made of rubber, fabric, and/or steel. Thus, at least collectively they form a composite structure.
During tire manufacturing, the individual components that form the carcass are often layered or placed on one another. Specifically, in an initial stage of manufacturing, the carcass is assembled by placing one or more plies or strips of a green rubber material onto a building drum. Some of the plies typically contain reinforcement strands or cords. Placement of the plies may generally involve stacking flat strips of various materials on the building drum and cutting the strips to length. The cut ends of the strips meet or overlap and create a splice or joint at one location. In this manner, a pair of sidewalls, a pair of apexes, an innerliner (for a tubeless tire), a pair of chafers, and a pair of gum shoulder strips may be placed on the building drum to construct the laminate structure that is the carcass. Additional components may be used or be substituted for some of the components mentioned above.
In subsequent processes, the carcass is transformed from a stack of flat strips into a green tire. Before this occurs, however, additional manufacturing steps may include folding a portion of the stack over the bead cores to form ply turnups. The carcass is eventually expanded into the toroidal shape at which point the reinforcing belts and the tread may be added. In the expanded state, the reinforcement threads in the plies generally run perpendicularly or radially to the centerline of the tire. For this reason, this type of tire is referred to as a “radial” tire. The resulting tire is made by curing the above-constructed green tire at a temperature and pressure sufficient to cure curable components. Building a tire by expanding an initially cylindrical carcass is not without manufacturing difficulties.
In view of difficulties with current tire manufacturing, an improved method for manufacturing tires and corresponding apparatus is sought. One method involves applying an elastomeric layer on a toroidal surface or core member and then placing and stitching a cord in continuous lengths onto the toroidal surface in a predetermined cord path. Each cord is essentially a string of one or more materials as opposed to being a flat sheet. The cords are stitched to the elastomeric layer while the path is followed. As such, the application process may include dispensing a cord from a spool thereof and guiding the cord in the predetermined path onto the core member. The core member may generally take the form of the tire, though smaller in size, and ultimately forms the inside surface of the resulting tire.
A system for stitching the cords to the elastomeric layer may include a tooling head and a means for positioning the tooling head relative to the core member, which may incrementally move as the core is stitched to the elastomeric layer. Bi-directional tooling heads are known to be used to stitch cords to a core member in a generally a side-to-side or radial looping pattern as the core member incrementally advances. Once all of the layers of cord are positioned, additional components, such as a belt-and-tread assembly, may be added to the stitched cord and elastomeric layer structure thereby forming a green tire. The green tire may undergo a similar curing operation as in conventional tire building. The cord application process, while effective, is not without its own challenges.
One such challenge is associated with maintaining an optimum amount of pressure between the cord and the elastomeric layer. Too little pressure may result in insufficient stitching and too much pressure may damage the cord or may damage the underlying elastomeric layer. Furthermore, consistent pressure application in conjunction with complex motions requires a specialized tooling head design.
In addition to difficulties with designing the tooling head itself, the ongoing problems with too little or too much pressure may be exacerbated by how the tooling head is positioned relative to the elastomeric layer or a previously applied cord. Attempts to utilize commercially available six-axis robots have been unsuccessful because placement accuracy, particularly at the speeds necessary to manufacture an economically viable tire, is unacceptable. Generally, the error in position is a result of a “stack-up” of errors for each individual axis to the application surface of the tooling head. Any stack-up is further magnified as the axes move to attempt to maintain the desired orientation of the tooling head with the toroidal surface. The overall result being an unacceptable degree of error that may result in the issues with cord placement and may damage the cord.
In addition to radial cord application, cords may be applied onto a tire-building surface in a geodesic pattern. Yet, geodesic patterns present a most-difficult pattern, particularly where the tire-building surface is defined by both concave and convex curves. The transition between curvatures creates application issues. For example, the cord may not be properly adhered to the surface in this region. For at least this reason, mass produced, affordable tires containing geodesic cord patterns have thus far eluded tire manufacturers.
A need, accordingly, remains for applicator assemblies and systems that are simple to construct, are operationally reliable, and are yet economically efficient while being accurate in application of a cord to a toroidal surface.